Critically ill patients should be susceptible to pulmonary thromboembolism (PTE). To determine the incidence of acute PTE in this patient population, we reviewed hospital charts and autopsy findings of all Class IV critically ill patients admitted to our hospital's Recovery Room-Acute Care Unit, between 1972 and 1982. Massive PTE either contributed to or was the sole cause of death in only two of the 152 patients studied (1.3%). Small single or scattered PTE were an incidental finding not contributing to morbidity or mortality in 13 patients. No gross evidence of PTE was found in the remaining 137 patients. There was no relationship between the occurrence of PTE and obesity, polycythemia, platelet count, PT or PTT, ventilatory support, level of PEEP, fluid balance, intravascular catheter days, pulmonary artery pressure, or pulmonary vascular resistance. Twelve patients did not have PTE at autopsy though it was seriously considered during ICU management. Unlike many other types of hospitalized patients, Class IV critically ill surgical patients are highly unlikely to suffer from PTE. When acute cardiorespiratory decompensation occurs, other more common causes should be given primary consideration.